The precise measurement of embryonic cardiovascular function has challenged investigators for more than a century. The primary experimental model for the investigation of cardiac morphogenesis has been the chick embryo, and despite the small size of the embryo chick heart, numerous investigators have developed experimental methods to accurately measure blood pressure, blood flow, and chamber size, and to alter cardiac function or form. The long term aim of the Physiology Core is to serve as a flexible resource for the experimental assessment of normal and altered cardiovascular development. the experimental model from this grant period os the stage 10 to 29 white Leghorn chick embryo, due to our extensive experience with this model. The specific aims of this Physiology Core are: Provide chick embryos, stages 10 to 29, for all experimental protocols defined in Projects #2, #3, and #4. Perform the integrated physiologic assessment of the embryonic cardiovascular system using techniques to define atrial, ventricular, and arterial function. Perform acute experiments to alter atrial and ventricular preload, time intervals, and afterload, and perform acute experiments to deliver drugs which stimulate or block calcium channels, B-receptors, the nitric oxide pathway, and atrial natriuretic peptide receptors. Perform acute experiments to decrease ventricular preload by vitelline vein banding, or left atrium partial ligation, and perform experiments to increase ventricular afterload by conotruncal banding or vitelline artery banding. Perform chronic experiments which involve drug delivery to stimulate or block calcium channels, B-receptors, the nitric oxide pathway, and atrial natriuretic peptide receptors, and to perform chronic experiments to alter ventricular preload or afterload. This Physiology Core will provide all of the resources necessary to perform and analyze the experiments proposed in Projects #2, #3, and #4. The experimental design of each project includes specific Guiding Hypotheses, proposed Experiments, and preliminary Interpretations. Resources are shared between the Physiology Core and the projects for maximum efficiency. Thus, the Physiology Core provides a state of the art resource for the design, execution, and analysis of experiments in the chick embryo model of cardiovascular morphogenesis. This integrated approach will provide crucial new information on the regulation of cardiovascular function. This integrated analysis then becomes the foundation for the structural and functional analysis of genetically altered cardiovascular systems in experimental models, and ultimately, aids in defining the underlying etiologies of congenital cardiovascular malformations.